Commercial turbine rotors typically include a plurality of axial blade attachments for receiving butt-ends of turbine blades. The axial blade attachments may include a plurality of steeples, each steeple having a series of grooves and hooks, thereby forming a “Christmas tree” or “fir tree” shape. The geometry of the steeples ensures a close mechanical linkage with the butt-ends of the turbine blades.
Over time, the turbine rotor steeples are subject to corrosion fatigue cracking. The cracks may prevent the proper operation of the turbine rotor. The cracking can be readily detected with several non-destructive testing (“NDT”) technologies. The NDT technologies include phased array ultrasonic and standard ultrasonic testing, which may be applied while the butt-end of the turbine blade is still attached to the rotor steeples, as well as eddy current, dye penetrant, and magnetic particle detection methods, which may be applied while the butt-end of the turbine blade is removed from the rotor steeples.
However, methods for removing the cracks have not kept pace with the improvements made in crack detection. Currently, detected cracks are ground out by hand, with a die grinder tool, or milled out with a milling machine to remove the cracked material down to a predetermined repair radius. Removal of the cracks by hand grinding and/or milling operations can be very tedious and time consuming. The time consuming repair process results in increased outage time for the turbine rotor, with an appreciable financial loss to the turbine operator, and decreased unit availability. Hand grinding and/or milling to remove the cracked material may result in a rough surface finish and various repair sites may have substantially different repair radii.
What is needed is an apparatus and method for more quickly removing the cracks in the turbine rotor steeples while at the same time maintaining or improving the quality control of the repair procedure.